'\" et
.TH TTY "1P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.\"
.SH NAME
tty
\(em return user's terminal name
.SH SYNOPSIS
.LP
.nf
tty
.fi
.SH DESCRIPTION
The
.IR tty
utility shall write to the standard output the name of the terminal
that is open as standard input. The name that is used shall be
equivalent to the string that would be returned by the
\fIttyname\fR()
function defined in the System Interfaces volume of POSIX.1\(hy2017.
.SH OPTIONS
The
.IR tty
utility shall conform to the Base Definitions volume of POSIX.1\(hy2017,
.IR "Section 12.2" ", " "Utility Syntax Guidelines".
.SH OPERANDS
None.
.SH STDIN
While no input is read from standard input, standard input shall be
examined to determine whether or not it is a terminal, and, if so, to
determine the name of the terminal.
.SH "INPUT FILES"
None.
.SH "ENVIRONMENT VARIABLES"
The following environment variables shall affect the execution of
.IR tty :
.IP "\fILANG\fP" 10
Provide a default value for the internationalization variables that are
unset or null. (See the Base Definitions volume of POSIX.1\(hy2017,
.IR "Section 8.2" ", " "Internationalization Variables"
for the precedence of internationalization variables used to determine
the values of locale categories.)
.IP "\fILC_ALL\fP" 10
If set to a non-empty string value, override the values of all the
other internationalization variables.
.IP "\fILC_CTYPE\fP" 10
Determine the locale for the interpretation of sequences of bytes of
text data as characters (for example, single-byte as opposed to
multi-byte characters in arguments).
.IP "\fILC_MESSAGES\fP" 10
.br
Determine the locale that should be used to affect the format and
contents of diagnostic messages written to standard error and
informative messages written to standard output.
.IP "\fINLSPATH\fP" 10
Determine the location of message catalogs for the processing of
.IR LC_MESSAGES .
.SH "ASYNCHRONOUS EVENTS"
Default.
.SH STDOUT
If standard input is a terminal device, a pathname of the terminal as
specified by the
\fIttyname\fR()
function defined in the System Interfaces volume of POSIX.1\(hy2017 shall be written in the following
format:
.sp
.RS 4
.nf

"%s\en", <\fIterminal name\fR>
.fi
.P
.RE
.P
Otherwise, a message shall be written indicating that standard input is
not connected to a terminal. In the POSIX locale, the
.IR tty
utility shall use the format:
.sp
.RS 4
.nf

"not a tty\en"
.fi
.P
.RE
.SH STDERR
The standard error shall be used only for diagnostic messages.
.SH "OUTPUT FILES"
None.
.SH "EXTENDED DESCRIPTION"
None.
.SH "EXIT STATUS"
The following exit values shall be returned:
.IP "\00" 6
Standard input is a terminal.
.IP "\01" 6
Standard input is not a terminal.
.IP >1 6
An error occurred.
.SH "CONSEQUENCES OF ERRORS"
Default.
.LP
.IR "The following sections are informative."
.SH "APPLICATION USAGE"
This utility checks the status of the file open as standard input
against that of an implementation-defined set of files. It is possible
that no match can be found, or that the match found need not be the
same file as that which was opened for standard input (although they
are the same device).
.SH EXAMPLES
None.
.SH RATIONALE
None.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
The Base Definitions volume of POSIX.1\(hy2017,
.IR "Chapter 8" ", " "Environment Variables",
.IR "Section 12.2" ", " "Utility Syntax Guidelines"
.P
The System Interfaces volume of POSIX.1\(hy2017,
.IR "\fIisatty\fR\^(\|)",
.IR "\fIttyname\fR\^(\|)"
.\"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
.PP
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
